The block diagram of automatic closed-loop adjustment of power factor. The main aim of adjustment of power factor is the variation of the field current. This is possible in a wound field machine. If the motor is opreated at a power factor of unity the current drawn by it will have the lowest magnitude for a given power input and therefore the lowest internal copper losses.

From this daigram the motor voltage and current are sensed and fed to the power factor calculator. The power factor calculator computes the phase angle between the two and therefore the power factor. It is the actual power factor value. The computed power factor value is compare against the power factor commanded value by using error detector . The   error is amplified by the error amplifier and its output varies the field current power factor confirmed to the commanded value.

PERMANENT MAGNET SYNCHRONOUS MOTOR DRIVES:

Permanent magnet sychronous motor are now commonly known as permanent magnet ac motors. They qre classfied according to the nature of voltage induced in the stator as sinusoidally excited and trapezoidally excited. These PMAC motor are commonly known as sinusoidal PMAC motors.

A sinuaoidal PMAC motor has diatributed winding synchronous in the stator side. It wmployed rotor geometrics such as inset or interior. Rotor poles are so shaped phase winding has a sinusoidal waveform.

 The stator of a trapezoidal PMAC motor has concentrated winding and a rotor with a wide pole arc. The voltage induced in the stator phase winding has a trapezoidal waveform. It employ rotor geometrics such as surface magnet. The speed of PMAC motors is controlled by feeding them from variable frequency voltage and current. They are operated in self controlled mode. Rotor position sensor are used for operation in self control mode of operation.

Different types of converters and inverter are used to drives the PMAC motors. The current trend is to use MOSFET for low voltage and low power application and IGBT for medium power applications. In the past self controlled mode of operation variable fequency drives employed a sinusoidal PMAC motor were also called brushless dc motor drives.  The energy aspect manage characteristic is executed with the aid of using sensing the section attitude among the motor voltage and current. This sign is fed again and as compared with a reference, and the distinction is used to feed the enter sign voltage to the six SCRs withinside the energy module.